In many electronic systems, a sensor (e.g., a pressure sensor) outputs a signal having a voltage representative of a condition (e.g., a pressure). An amplifier multiplies the signal by a gain to create an input signal for the A/D converter. Prior systems typically adjust the gain of the input amplifier based on the analog signal input to the amplifier. For example, U.S. Pat. Nos. 3,187,323, 3,958,178, 4,105,967, 4,305,063, 4,605,920, and 6,288,664, describe systems in which the analog input signal is used in the gain selection circuit.
In many cases, external hardware/software components and/or additional circuitry may be required for various applications. For example, in U.S. Pat. No. 3,790,886, Kurtin et al. describe an A/D converter that utilizes mode switches, an active rectifier/polarity sensor, and a dual slope conversion to measure the magnitude of an unknown input voltage source.
In U.S. Pat. No. 4,901,078, Goyal describes an A/D converter that utilizes a differential method and circuitry so that the magnitude of the difference between the input and offset voltages fall in the input range of the A/D converter.
In U.S. Pat. No. 5,170,166, Tanaka et al. disclose a range switching device that uses two A/D converters for analog to digital conversion in which an analog signal from a photoelectric component is amplified by a switching amplifier. The amplified signal is forwarded to two A/D converters—a measuring A/D converter and a switching A/D converter. The switching A/D converter converts the analog signal to a digital signal. The digital signal from the switching A/D converter is compared with the upper and lower limits of the measuring A/D converter to determine the required amplification change for the switching amplifier.
In U.S. Pat. No. 5,194,865, Mason et al. disclose an A/D converter having an automatic range control. The converter of Mason et al. includes a level shifter for adjusting the magnitude of an analog signal into the A/D converter. The level shifter requires the use of a peak detector circuit for generating a reference potential corresponding to a peak amplitude of the analog signal to be converted.
In U.S. Pat. No. 5,329,281, Baumgartner et al. describe an PAD converter that utilizes an offset subtraction. Additional circuitry associated with the offset subtraction is required to implement the A/D converter of Baumgartner et al.
In U.S. Pat. No. 5,568,143, Hutchinson et al., disclose an analog to digital conversion system with an automatically and dynamically variable resolution range. In the system of Hutchinson et al., a microprocessor operates an A/D converter to sample an integrator output at successive increments of time. The digitized samples from the A/D converter are compared with a predetermined value in the upper end of the amplitude range of the A/D converter. Low amplitude analog signals do not reach the predetermined level until the later sampling times and thus are resolved at the upper end of the resolution range. Higher amplitude analog signals are resolved at the lower end of the resolution range. Thus, the resolution dynamically and automatically increases inversely with the amplitude of the analog signal being digitized. The digitized value is expressed by two binary numbers, one corresponding to the number of samples until detection of the sample of the integrator output achieving the predetermined amplitude, and the other corresponding to the value which the integrated signal has achieved.
In U.S. Pat. No. 5,844,512, Gorin et al. describes an autoranging device that utilizes a gain detector to set the gain of a variable operational amplifier prior to sending the op-amp output to the A/D converter. The device of Gorin et al. requires the gain detector and an amplifier gain setting rule processor in parallel with an anti-aliasing filter.
In U.S. Pat. No. 6,140,948, Yu describes an A/D converter system that uses two banks of capacitors. More specifically, a first bank of capacitors samples a reference voltage and a second bank of capacitors simultaneously samples a second input voltage. Thus, a reference voltage and two banks of capacitors are required to implement the A/D converter system of Yu.
In U.S. Pat. Nos. 6,414,619 and 6,590,517, Swanson describes an autoranging A/D converter that utilizes two inputs: an analog input and an estimate of the analog input. The autoranging A/D converter of Swanson also requires the use of an offset.
In U.S. Pat. No. 6,683,552, Noll et al. describe a converter system that requires the use of two A/D converters and a multiplexer. The converter system of Noll et al. requires merger of the corrected data from the two A/D converters.
In U.S. Pat. No. 6,864,820, Nakamura describes a method for extending the range of an A/D converter. The amount of overrange is determined using a special circuit and then compensated by offsetting. The method of Nakamura does not use a change in the gain of an operational amplifier.
In U.S. Pat. No. 6,940,445, Kearny describes a programmable input voltage range A/D converter. However, this programmable input range A/D converter does not control the output of an operational amplifier.
In U.S. Pat. No. 6,993,291, Parssinen et al. describe a method for controlling the range of an A/D converter. The control method of Parssinen et al. is not applicable to A/D converters of which the range is fixed.
In U.S. Patent Application Publication No. 2003/0102994, Stimmann describes a range converter that takes a signal source from a transducer and feeds it into an amplifier bank. In Stimmann, a bank of comparators is required to determine which channel in the amplifier bank is within the range of the A/D converter.